NOAA/WDS Paleoclimatology - Global sediment trap calibration of Mg/Ca in G. ruber white, with associated temperature, salinity and carbonate system data

The Mg/Ca of planktic foraminifera Globeriginoides ruber (white) is a widely applied proxy for tropical and sub-tropical sea-surface temperature. The accuracy with which temperature can be reconstructed depends on how accurately relationships between Mg/Ca and temperature and the multiple secondary controls on Mg/Ca are known; however, these relationships remain poorly quantified under oceanic conditions. Here, we present new calibrations based on 440 sediment trap/plankton tow samples from the Atlantic, Pacific and Indian Oceans, including 130 new samples from the Bay of Bengal/Arabian Sea and the tropical Atlantic Ocean. Our results indicate temperature, salinity and the carbonate system all significantly influence Mg/Ca in G. ruber (white). We propose two calibration models: The first model assumes pH is the controlling carbonate system parameter. In this model, Mg/Ca has a temperature sensitivity of 6.0±0.8 %/°C (2s), a salinity sensitivity of 3.3±2.2 %/PSU and a pH sensitivity of -8.3±7.7 %/0.1 pH units; The second model assumes carbonate ion concentration ([CO32-]) is the controlling carbonate system parameter. In this model, Mg/Ca has a temperature sensitivity of 6.7±0.8 %/°C, a salinity sensitivity of 5.0±3.0 %/PSU and a [CO32-] sensitivity of -0.24±0.11 %/µmol kg-1. In both models, the temperature sensitivity is significantly lower than the widely-applied sensitivity of 9.0±0.6 %/°C. Application of our new calibrations to down-core data from the Last Glacial Maximum, considering whole ocean changes in salinity and carbonate chemistry, indicate a cooling of 2.4±1.6 °C in the tropical oceans if pH is the controlling parameter and 1.5±1.4 °C if [CO32-] is the controlling parameter.